In the past it was difficult to determine the performance characteristics of an engine due to the fact that it was difficult to determine what was taking place in the combustion chamber of the engine. With the advent of ion sensing came the ability to determine the characteristics of the combustion within a combustion chamber, allowing one to determine whether a fuel mixture was, for example, too rich or too lean or whether knocking or good combustion was taking place.
Ion sensing relies on the fact that combustion in an engine creates measurable ionized gas. In such an engine an ion sensor may be installed or, with proper circuitry, the ignition spark plug or ignition coil may be used to sense ion current without installing additional sensors. The ion sensor detects a small current that flows through the ionized gas in the combustion chamber, and amplifier circuitry is used to allow analysis of the combustion ion signal to diagnose engine performance characteristics.
To provide enhanced analysis of the ion current signal, electronics are being integrated into ion sensing ignition coils for amplifying the small ion current signal and transmitting a high level analog signal to the Engine Control Unit (ECU) or other engine monitoring systems. Indeed, one such system is disclosed in co-pending application Ser. No. 12/714,975, filed on even date herewith, entitled Automatic Variable Gain Amplifier and assigned to the assignee of the instant application, the teachings and disclosure of which are hereby incorporated in their entireties by reference thereto.
One problem that has become apparent in ion sensing, however, relates to powering both the ion sensor, be it the ignition coil (spark plug) or a separate sensor, and the amplifying or signal processing electronics used therewith. In order to generate an ion current, the circuit requires a high voltage bias supply, in the range of 200 to 400 volts DC. The electronics used to amplify this ion signal also requires power, typically +/−5 Vdc.
In order to supply this power to these circuits, additional wires must be included in the system wiring harness. Such additional wires add to the overall cost and complexity of the system and the coil circuitry. Supplying this voltage to the ion sensing ignition coils though requires careful attention to ground loops and wire routing. Additionally, an Electromagnetic Interference (EMI) filter must be present inside each coil to filter any EMI that may be picked up by the system harness. Moreover, the typical voltage available in an engine system is 12 to 24 volts DC.
Further, generating the 200 to 400 volt bias required for the ion current generation is difficult. In the past, the bias would have been created using a flyback DC to DC converter containing a step up transformer. Because the bias current requirements are very low, the DC-DC converter could be small and contained in each coil. However, since the coils operate on the engine, their normal operating temperature is in the range of 90 to 100° C. Transformers of the typical DC-DC converter grade ferrites cannot operate at these high temperatures. Thus, higher cost ferrites, able to operate under the high temperature conditions, would need to be used, but this would drive up cost. Alternatively, the system could utilize a larger single DC-DC converter mounted off the engine to supply voltage to each coil, however this would require additional system harness wiring, again driving up cost and complexity. Moreover, the designer would be required to be cautious so as not to create ground loops, and isolation amplifiers would most likely be required. This, again, would increase cost and complexity.
Therefore, it would be advantageous to provide a system to supply the voltages required by the ion sensing ignition coils and electronics without adding the complexity and cost of additional wiring, high cost DC-DC ferrites, or a DC-DC converter mounted off of the engine. Additionally, it would be advantageous to provide an ignition system with ion sensing ignition coils that does not require EMI filters in the coils and eliminates the risk and complexity associated with possible ground loops created by the harness. Moreover, it would be advantageous to provide ion sensing ignition coil circuitry that is simple, small in size, operable at the high engine temperature.
Embodiments of the present invention provide such a system that provides one or more of the above advantages. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.